1. Field of the Invention
The present invention relates to a buckle apparatus for fixing a tongue plate used at a seat belt apparatus of a vehicle.
2. Description of the Related Art
A webbing belt structures a seat belt apparatus for restraining the body of an occupant sitting in a seat of a vehicle. One end portion in a longitudinal direction of the webbing belt is engaged with, for example, a winding shaft of a winding apparatus provided at a side of the seat. The other end portion is fixed at an anchor plate provided at a vicinity of the winding apparatus. A longitudinal direction central portion of the webbing belt passes through, for example, an insertion hole of a through-anchor provided upward of the winding apparatus, at an upper side of a center pillar of the vehicle, and is turned downward.
The webbing belt, between the portion that turns down at the through-anchor and the other end, passes through an insertion hole of a tongue plate. When this tongue plate is pulled on, the webbing belt wound around the winding shaft of the winding apparatus is pulled out. When the tongue plate is coupled with a buckle apparatus, which is provided at a side of the seat opposite to a side thereof at which the winding apparatus is disposed, the webbing belt is in an engaged state.
Some vehicles are equipped with a warning mechanism which, when an occupant is sitting in the seat but the webbing belt is not in the engaged state, lights up an indicator or the like provided at an instrument panel of the vehicle or the like, and warns that the webbing belt is not engaged.
As an example of this warning mechanism, a structure has been devised which detects movement of a latch inside a buckle apparatus or of a tongue plate inserted into a buckle apparatus, or the like.
Further, a structure has been devised in which, in this sort of warning mechanism, a permanent magnet is provided at an ejector which moves when pressured by the latch or by the tongue plate inserted into the device main body, and a magnetic sensor (an MRE element, a Hall element or the like) is provided at a predetermined position inside the buckle apparatus. Due to movement of the permanent magnet in accordance with movement of the latch or ejector, a change in a magnetic field is detected by the magnetic sensor.
However, a space in which members such as the permanent magnet and the like can move in the extremely limited space inside the buckle apparatus is extremely small. Moreover, when the permanent magnet is moved with the latch or the ejector, a displacement amount of the permanent magnet is small. Consequently, the change in the magnetic field of the permanent magnet that is to be detected by the magnetic sensor is small. Therefore, if mounting accuracy of the magnetic sensor and the permanent magnet is not very strict, movement of the latch or ejector cannot be reliably detected by the magnetic sensor.